With his just-announced opposition to the proposed sales tax hike to fund transportation projects in Missouri, Gov. Jay Nixon has further cemented his membership in The Party of One.

Nixon’s opposition will enrage unions and other traditional allies in his Democratic Party. They had thought they could count on the governor’s cooperation. According to sources, Nixon had all but promised as much last year.

But that was then and this is now. I’m not a mind reader, but several factors undoubtedly played into Nixon’s announcement.

First, the General Assembly’s tax policy is horrible. On that point Nixon is absolutely correct. Who in their right mind passes an income tax cut that mostly benefits the rich and certain types of businesses, and then turns around and asks voters to pay an extra three-quarters of a cent for most things they purchase so that the state can have enough money to fix and maintain its roads?

Missouri lawmakers, of course. Their proposed tax hike may be the worst mixed message to ever come out of Jefferson City.

Second, I suspect Nixon is feeling vengeful. The legislature mustered the votes to override his veto of the income tax cut bill, and relationships between the governor and legislators have never been more polluted. If lawmakers want to walk the plank with a disastrous sales tax proposal, Nixon probably figures that no only does he not need to join them, he might as well give them a shove.

And third, Nixon really doesn’t care if he’s a party of one. He’s probably not running for office again in Missouri. At this point, he has nothing to lose by standing up for ordinary Missourians against the special interests.

I actually agree with everything Nixon says in his statement of opposition. Even this sentence: “If this effort is successful, Missouri will have the dubious distinction of being a state that, in a matter of months, cut taxes on lawyers and lobbyists, but hiked taxes on bar soap and baseball gloves.”

(Baseball gloves?)

But, as Nixon says, the state is long overdue for “a robust discussion about Missouri’s long-term transportation infrastructure needs.” As governor, he’s supposed to be leading that conversation, but he isn’t. Expressing principled opposition against an unwise proposal put forth by others is not the same as rallying people around a good idea.